Abstract

Metabolic phenotype can be affected by multiple factors, including allelic variation and interactions with inhibitors. Human CYP2D6 is responsible for approximately 20% of cytochrome P450–mediated drug metabolism but consists of more than 100 known variants; several variants are commonly found in the population, whereas others are quite rare. Four CYP2D6 allelic variants—three with a series of mutations distal to the active site (*34, *17-2, *17-3) and one ultra-metabolizer with mutations near the active site (*53), along with reference *1 and an active site mutant of *1 (Thr309Ala)—were expressed, purified, and studied for interactions with the typical substrates dextromethorphan and bufuralol and the inactivator SCH 66712. We found that *34, *17-2, and *17-3 displayed reduced enzyme activity and NADPH coupling while producing the same metabolites as *1, suggesting a possible role for Arg296 in NADPH coupling. A higher-activity variant, *53, displayed similar NADPH coupling to *1 but was less susceptible to inactivation by SCH 66712. The Thr309Ala mutant showed similar activity to that of *1 but with greatly reduced NADPH coupling. Overall, these results suggest that kinetic and metabolic analysis of individual CYP2D6 variants is required to understand their possible contributions to variable drug response and the complexity of personalized medicine.

Footnotes

Received December 15, 2017.

Accepted May 9, 2018.

This work was supported by the National Institutes of Health (L.L.F.) [Grant 1R15GM086767-02, -03 and -02S1]; a grant to Kalamazoo College from the Howard Hughes Medical Institute [52006304] through the Precollege and Undergraduate Science Education Program; and the Cook, Kaufmann, Hutchcroft, and Varney Funds of Kalamazoo College.

This work was presented in part at the American Society for Biochemistry and Molecular Biology annual meeting, 2016, San Diego, CA, and 2017, Chicago, IL, and at the Great Lakes Drug Metabolism and Disposition Meeting, 2017, Kalamazoo, MI.